International Journal of Engineering Trends and Technology (IJETT) – Volume 4 Issue 7- July 2013
Two-Diode Model Performance Analysis of
Photovoltaic Panels
ġaban Yılmaz #1, Alev Yılmaz *2, Mahit GüneĢ *3 Hasan Rıza Özçalık #4
#
Kahramanmaras Sutcu Imam University1,
Kahramanmaraş / Turkey
Abstract— Using of photovoltaic systems is increasing continuously
today, modeling of solar cells is very important as to design the
systems more efficiently that requires for the success of simulation
studies. Two-diode equivalent circuit is developed and successful
model.
To model the photovoltaic (PV) solar cells using two-diode
equivalent circuit and comparison of characteristics of catalog
values of current voltage and power voltage is the main subject of
the article. The model which was created with the help of Matlab is
examined how the characteristics will be solar radiation at 1000
w/m2 and 25 °C ambient temperatures.
Keywords: Photovoltaic (PV), Solar Energy, Matlab, two-diode
model.
I. INTRODUCTION
The increasing of the productivity in the new generation
photovoltaic systems day by day and decreasing in the cost is
increased the using of photovoltaic systems significantly.
Photovoltaic systems not only the economical energy source for
the limited applications like in the past but also becoming an
alternative energy source to the traditional methods and
producing energy at the range of GWh.
Photovoltaic systems have been the focus of attention because
of being environmentally, renewable and long lasting. Planning
of photovoltaic systems must be modelled to be planned and
optimal using in order to be used optimum.
A solar cell is an electronic device which directly converts
sunlight into electricity. Light shining on the solar cell produces
both a current and a voltage to generate electric power. This
process requires firstly, a material in which the absorption of light
raises an electron to a higher energy state, and secondly, the
movement of this higher energy electron from the solar cell into
an external circuit. The electron then dissipates its energy in the
external circuit and returns to the solar cell. A variety of materials
and processes can potentially satisfy the requirements for
photovoltaic energy conversion, but in practice nearly all
photovoltaic energy conversion uses semiconductor materials in
the form of a p-n junction.
The generation of current in a solar cell, known as the "lightgenerated current", involves two key processes. The first process
is the absorption of incident photons to create electron-hole pairs.
Electron-hole pairs will be generated in the solar cell provided
ISSN: 2231-5381
that the incident photon has energy greater than that of the band
gap. However, electrons (in the p-type material), and holes (in the
n-type material) are meta-stable and will only exist, on average,
for a length of time equal to the minority carrier lifetime before
they recombine. If the carrier recombines, then the lightgenerated electron-hole pair is lost and no current or power can
be generated.
A second process, the collection of these carriers by the p-n
junction, prevents this recombination by using a p-n junction to
spatially separate the electron and the hole. The carriers are
separated by the action of the electric field existing at the p-n
junction. If the light-generated minority carrier reaches the p-n
junction, it is swept across the junction by the electric field at the
junction, where it is now a majority carrier. If the emitter and
base of the solar cell are connected together (i.e., if the solar cell
is short-circuited), the light-generated carriers flow through the
external circuit [30].
Figure 1: Cross section of a solar cell [30].
During the last decades, different approaches have been
developed in order to identify electrical characteristics of both
models. (Castaner & Silvestre, 2002) have introduced and
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evaluated two separate models (one-diode and two-diode models)
for a solar cell but dependency of the models parameters on
environmental conditions has not been fully considered. Hence,
the proposed models are not completely accurate. (Sera et al.,
2007) have introduced a photovoltaic panel model based on
datasheet values; however with some restrict assumptions. Series
and shunt resistances of the proposed model have been stated
constant and their dependencies on environmental conditions
have been ignored. Furthermore, dark-saturation current has been
considered as a variable which depend on the temperature but its
variations with irradiance has been also neglected. Model
equations have been merely stated for a solar panel which
composed by several series cells. (De Soto et al., 2006) have also
described a detailed model for a solar panel based on data
provided by manufacturers. Several equations for the model have
been expressed and one of them is derivative of open-circuit
voltage respect to the temperature but with some assumptions.
Shunt and series resistances have been considered constant
through the paper; also their dependency over environmental
conditions has been ignored. Meanwhile, only dependency of
dark-saturation current to temperature has been considered.
(Celik & Acikgoz, 2007) have also presented an analytical onediode model for a solar panel. In this model, an approximation
has been considered to describe the series and shunt resistances;
they have been stated by the slopes at the open-circuit voltage
and short-circuit current, respectively. Dependencies of the model
parameters over environmental conditions have been briefly
expressed. Therefore, the model is not suitable for high accuracy
applications. (Chenni et al., 2007) have used a model based on
four parameters to evaluate three popular types of photovoltaic
panels; thin film, multi and mono crystalline silicon. In the
proposed model, value of shunt resistance has been considered
infinite. The dark-saturation current has been dependent only on
the temperature. (Gow & Manning, 1999) have demonstrated a
circuit-based simulation model for a photovoltaic cell. The
interaction between a proposed power converter and a
photovoltaic array has been also studied. In order to extract the
initial values of the model parameters at standard conditions, it
has been assumed that the slope of current-voltage curve in opencircuit voltage available from the manufacturers. Clearly, this
parameter is not supported by a solar panel datasheet and it is
obtained only through experiment [32].
II. MATERIAL AND METHOD
Mathematical descriptions of the I-V characteristics of PV
cells are available since many years and are derived from the
physics of the p-n semiconductor junction.
A crystalline solar cell is, in principle, a large-area silicon
diode. In the dark state, the I-V characteristic curve of this diode
corresponds to the one of a normal p-n junction diode and it
produces neither a voltage nor a current.
Illumination of the PV cell creates free charge carriers, which
allow current to flow through a connected load. The so called
photocurrent IL is proportional to irradiance. If the circuit is open
the photocurrent is shunted internally by the p-n junction diode
[31].
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The single diode equation assumes a constant value for the
ideality factor n. In reality the ideality factor is a function of
voltage across the device. At high voltage, when the
recombination in the device is dominated by the surfaces and the
bulk regions the ideality factor is close to one. However at lower
voltages, recombination in the junction dominates and the ideality
factor approaches two. The junction recombination is modelled
by adding a second diode in parallel with the first and setting the
ideality factor typically to two[30].
TABLE I
PHOTOVOLTAIC PARAMETERS
Rs
Series Resistance
Ipil
PV Battery Output Current
Rp
Parallel Resistance
VD
Diode Voltage
q
Electron Load
Gref
N.Amount of Solar Radiation
m
Ideality Factor
G
Amount of Solar Radiation
k
Boltzmann Constant
Isc
Nom. Short-Circuit Current
T
Kelvin Temperature
Voc
Nom. Open Circuit Voltage
Npc
Number of Parallel
IM
Max. Power Point Current
Nsc
Number of Serial
Tref
Nominal Operating Temp.
PM
Maximum Power
VM
Max. Power Point Voltage
C0
Temperature Coefficient
Kv
Voltage Temp. Coefficient
ID
Diode Current
Ie
Electron Current
Iph
Photovoltaic Current
Ih
Hole Current
Ish
Parallel Resistor Current
Ki
Current Temp. Coefficient
Ioref
Reference Current
Eg
Diodes Bandwidth
b
Constant Semiconductor
I0
Diode Saturation Current
Figure 2: Photovoltaic solar battery two-diode equivalent current [4, 7, and 9]
The two diodes equivalent circuit is used modeling
photovoltaic solar cells. The diode models are more successful
due to equivalent circuit which is seen in figure 2. In figure 2 Rs
and Rp is shown the effecting of efficiency of the serial and
parallel resistors of the module. While the crystal defects creates
parallel resistor, the metal contacts which is effected on
semiconductor material, the internal resistance of the layers of
semiconductor material, the metallic piece which is on the
surface of the module forms the resistance. The effect of the
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parallel resistance is a factor that reduces open circuit voltage and
fill factor of the module. The effect of series resistance is a factor
that reduces short-circuits current and fill factor of the module [1].
If Kirchhoff current law is applied on the circuit in figure 1;
(9)
(1)
The net election current and hole current with Boltzman
distribution [2];
(10)
(2)
(3)
(11)
(4)
q: Electron Load (1.602×10-19 C),
k: Boltzmann Constant (1.381×10-23 J/K)
The solar cell equivalent circuit which is shown in figure 1
source current expression is gotten in equation 5 by applying
Kirchhoff’s voltage law.
(5)
Eq. (9) is performed by using of Eqs. (10-11) to obtain current of
solar cell [1,3,4]
Graph showing the double diode model. The device in gray has
no parasitic resistance losses. The device in red has the loss of
series and shunt resistance included [30].
Solar panels are consists of NPC numbers of parallels panels.
Each Npc line is connected in series with each other. The total
value of the voltage of photovoltaic which is connected in series
to each other calculates by adding together of the current value of
each photovoltaic. The total current value of the photovoltaic
which is connected in parallel to each other, calculates adding
together the current value of that is produced for the same voltage
value [2, 3].
Vm, the voltage which is applied to the end of the module
Im, module current
VM=Nsc. Vnew
(6)
IM=Npc. Inew
(7)
(8)
Figure 3: The effect of the parameter-1
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Figure 4: The effect of the parameter-2
Figure 6: The effect of the parameter-4
Figure 5: The effect of the parameter-3
Figure 7: The effect of the parameter-5
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III. PHOTOVOLTAIC MODELLED PARAMETERS
All paragraphs must be indented. All paragraphs must be
justified, i.e. both left-justified and right-justified.
Label values of Sharp NT-S5E1U type photovoltaic panels are
power of 185, 0 W, Vmp=36, 21 V, Imp=5, 11 A, Voc=45, 9 V,
Isc=5.75 A, W=15, 5 kg, 1580x808x35 (mm), mono-Si. This type
panel values are applied to our model.
IV. RESULTS
The model which was created with the help of Matlab is
examined how the characteristics will be solar radiation at 1000
w/m2 and 25 °C ambient temperatures.
The power voltage characteristics of photovoltaic panel in
figure 8, the modal and actual value is seen be very close to each
other. For the value of Vmp=36, 21 V PModel =180,301 Watt and
PREAL =186,552 Watt. The fail is %3.22
Current –voltage characteristic of photovoltaic panel in figure
10, the model and the actual value is seen be very close to each
other. For the value of Vmp=36, 21 V, IModel =5,118 Ampere IREAL
(ACTUAL) =5,182 Watt. The fail is %1, 23
As a result, in the simulation studies which is necessary for
photovoltaic systems the two –diode model can be used
successfully to model of photovoltaic model.
Figure 10: Current – Voltage Characteristics
Figure 8: Power-Voltage Characteristics
Figure 9: The difference of Power voltage characteristic
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Figure 11: The difference of Current- Voltage characteristic.
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